(i) Field of the Invention
The present invention relates to the fields of aquiculture and pisciculture, and relates in particular to breeding farms where an ozone treatment is carried out of all or some of the water which supplies the breeding basin(s) of the user site.
(ii) Description of the Related Art
Ozone treatment of such breeding farms has been the subject of a very abundant literature. Reference may be made for example to French patent application in the name of the Applicant FR-99 06567 which relates to the ozonation of breeding farms operating in a closed circuit. Underlying the considerable importance of treating the water which supplies the basins (sanitation, productivity and the like), difficulties and questions remain regarding the use of ozonation treatments. This is linked, in particular, to the fact that the residual species from an ozone treatment can be toxic for the species raised, whether this is the ozone residue itself in the medium or, alternatively, all of the oxidizing by-products derived from the oxidation reactions of the ozone on the medium (in particular on seawater)
The existing solutions, reported in the literature (active charcoal filter, xe2x80x9cstrippingxe2x80x9d and the like), for removing these traces of ozone or of oxidizing by-products are not very satisfactory in the context of the pisciculture, and in particular for the ozone treatment of seawater. This is either because the cost of exploiting them is high, or because they are unprofitable for high outputs of water to be treated, or quite simply because they are inapplicable to seawater.
One of the objectives of the present invention is therefore in particular to provide a method which makes it possible to improve the conditions for the breeding of fish and other sea products (pisciculture and aquiculture), using an ozone treatment of all or some of the water which supplies the breeding basins. The method is applicable to both seawater and freshwater breeding. The method is applicable to breeding farms operating in a closed circuit or in an open circuit. One of the intended aims is not to be limited in the levels of ozone treatment which are applied, while providing real safety for the species raised.
The present invention therefore relates to a method of improving the breeding conditions in pisciculture or aquiculture. The breeding is of the type where an ozone treatment is carried out on all or some of the water which supplies at least one breeding basin. The method involves carrying out a chemical treatment of the stream of ozonated water which supplies the breeding basin, before it reaches the basin. The method involves addition of a reducing chemical species, in order to carry out the substantial removal of the possible oxidizing by-products of the treatment of the water with ozone, and/or of the ozone residue in the water, in the following manner:
the reducing chemical species is added in situ and continuously on a line which is connected at its downstream part to the breeding basin and at its upstream part to a point where the ozonation treatment of the stream of water is carried out.
The method according to the invention can also adopt one or more of the following characteristics:
an evaluation of the content of dissolved ozone and/or of oxidizing by-products in the water is carried out, downstream of the point of addition of the reducing species, and retroactive action is taken where appropriate, according to the result of this evaluation, on the conditions for addition of the reducing species to the stream of water;
an evaluation of the content of dissolved ozone and/or of oxidizing by-products in the water is carried out, upstream of the point of addition of the reducing species, and the conditions for addition of the reducing species are regulated according to the result of the evaluation;
the addition of the reducing chemical species is adjusted according to the level of ozonation of the stream of ozonated water, the adjustment being carried out at the stoichiometric level;
an evaluation of the content of dissolved ozone and/or of oxidizing by-products in the water is carried out, downstream of the point of addition of the reducing species, the evaluation being carried out with the aid of a system operating on the principle of the redox potential, in order to provide a relative value capable of triggering, depending on the result of the evaluation, an alarm and/or a retroaction on the conditions for addition of the reducing species;
the point where the ozonation treatment is carried out is provided with one or more of the following components: a component for on-line gas/liquid transfer such as a static mixer or a hydroinjector, and a contact-maker such as a contact tower;
the breeding farm operates in a closed circuit, according to which:
a) at least some of the water of at least one breeding basin is recycled, which recycled water undergoes one or more purification treatments before being reinjected into the basin considered;
b) on the recycling path of step a), the recycled water is mixed with a supply of fresh water;
c) an ozonation of all or some of the recycled water is carried out, and furthermore where appropriate an ozonation of all or some of the supply of fresh water is carried out before it is mixed with the recycled water;
the addition of the reducing chemical species being carried out in the water recirculation circuit, downstream of the point where the ozonation is carried out.
The breeding farm operates in a closed circuit, according to which:
a) at least some of the water of at least one breeding basin is recycled, which recycled water undergoes one or more purification treatments before being reinjected into the basin considered;
b) on the recycling path of step a), the recycled water is mixed with a supply of fresh water;
c) an ozonation of all or some of the supply of fresh water is carried out before it is mixed with the recycled water;
the addition of the reducing chemical species being carried out in the supply of ozonated fresh water before it is mixed with the recycled water, or alternatively in the mixture of recycled water and of ozonated fresh water, before this mixture reaches the breeding basin.
the addition of the reducing species is carried out by metered additions, to the stream of water to be chemically treated, of a solution of a salt of the reducing species.
Other characteristics and advantages of the invention will emerge from the following description, given solely by way of illustration and with no limitation being implied, and made with reference to the appended drawings.